Image enhancement in 26 GHz-band 1-bit direct digital RF transmitter using manchester coding

In this paper, we propose a direct digital RF transmitter with a 1-bit band-pass delta-sigma modulator (BP-DSM) that uses high order image components of the 7^th Nyquist zone in Manchester coding for microwave and milimeter wave application. Compared to the conventional non-return-to-zero (NRZ) coding, in which the high order image components of 1-bit BP-DSM attenuate severely in the form of sinc function, the proposed 1-bit direct digital RF transmitter in Manchester code can improve the output power and signal-to-noise ratio (SNR) of the image components at specific (4n-1)^th and (4n-2)^th Nyquist Zone, which is confirmed by calculating of the power spectral density. Measurements are made to compare three types of 1-bit digital-to-analog converter (DAC) signal in output power and SNR; NRZ, 50% duty return-to-zero (RZ) and Manchester coding. By using 1 V_pp/8 Gbps DAC output, 1-bit signals in Manchester coding show the highest output power of −20.3 dBm and SNR of 40.3 dB at 7^th Nyquist Zone (26 GHz) in CW condition. As a result, compared to NRZ and RZ coding, at 7^th Nyquist zone, the output power is improved by 8.1 dB and 6 dB, respectively. Meanwhile, the SNR is improved by 7.6 dB and 4.9 dB, respectively. In 5Mbps-QPSK condition, 1-bit signals in Manchester code show the lowest error vector magnitude (EVM) of 2.4% and the highest adjacent channel leakage ratio (ACLR) of 38.2 dB with the highest output power of −18.5 dBm at 7^th Nyquist Zone (26 GHz), respectively, compared to the NRZ and 50% duty RZ coding. The measurement and simulation results of the image component of 1-bit signals at 7^th Nyquist Zone (26 GHz) are consistent with the calculation results.